Ion exchange of glass fibers



United States Patent 01 lice 3,332,135 Patented May 7, 1368 3,382,135 ION EXHANGE F GLASS FEBERS Richard G. Adams, Upper Montclair, N..l., assignor to .l. P. Stevens & Co., Inc, New York, N.Y., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 284,220, May 29, 1963. This application Aug. 11, 1966, Ser. No. 571,732 v 8 Claims. (Cl. 16193) ABSTRACT OF THE DISCLOSURE This invention concerns a process for treating a sized fibrous siliceous substrate such as glass fabric with polyvalent metal cations, or a mixture of polyvalent metal cations with alkali metal cations, prior to thermal desizing so that the resultant desized fabric has good whiteness and retains a substantial portion of its original greige strength.

This is a continuation-in-part of application Serial No. 284,220, filed May 29, 1963 now abandoned.

This invention concerns processes for preparing fibrous siliceous materials having improved physical properties and the products resulting therein.

More particularly, this invention relates to improving the thermal and tensile properties of fibrous siliceous substrates through thermally induced ion exchange techniques.

The term fibrous as used herein, particularly when used to describe glass (or silica), is used in contradistinction to massive, cast glass or any other nonfibrous siliceous material which possesses little or no applicability to the fabrication of fabrics or textiles. The term includes fibers, yarns, threads, ends, rovings and filaments or any other fiber form used in the preparation of textiles.

The term siliceous as used herein is used in its generic sense so as to include glass, quartz and related substrates.

During the production of siliceous fibers such as glass, the fibers are exposed to various stresses due to friction and abrasion incurred during processing.

These stresses can lead to considerable wear and breakage in the final product if unchecked.

In order to minimize destructive breakage and wear during processing it is customary in the industry to treat the fibers with a protective lubricant or binder material referred to as a size. Generally, this material is applied in the form of an aqueous dispersion while the fibers are being drawn out. Sizing usually consists of lubricating oils of natural or synthetic origin, starch, incorporated with small quantities of adjuvants such as surfactants, dispersing agents and the like.

After the sized fibers are woven, knitted or otherwise fabricated into a fibrous material, textile or cloth, the sizing interferes with further processing and is undesirable. For example, the sizing interferes with various operations such as coloring, laminating and finishing. Because of its effect on finishing operations, it is important that the substrate be desized with as little reduction in the finished products strength as possible.

Sizing can be removed with either chemical or thermal treatment. However, the present chemical treatments are disadvantageous in several respects. For example, they are time consuming and hence costly, and they do not readily produce an acceptable product. In addition chemical desizing does not permit weave setting as is possible with thermal treatments. For these reasons chemical desizing is seldom satisfactorily employed.

Thermal desizing procedures are often classified as high or low temperature according to the process temperature utilized. In most low temperature processes the sized fibrous substrate is heated between about 500 and 700 F. and the size slowly volatilized from the fabric by maintaining the fabric in the temperature environment for between about 55 and hours. A good white product is obtained but at the expense of a considerable decrease in tensile strength of the fired product. Further, weave setting which is a desirable attribute of thermal desizing processes cannot be achieved much below temperatures of about 900 F.

High temperature desizing is generally accomplished by exposing the sized substrate to temperatures between about 1100 F. to about 1300 F. for very short treatment times, usually for about 210 seconds. The high temperature desizing is advantageous in that it gives rise to a very white weave set product.

Unfortunately, this exposure to high temperatures, albeit for short times, gives rise to a product possessing low tensile strength, in most instances between about 30 to 60% of the greige strength. This loss of strength in both types of thermal desizing is obviously undesirable, particularly since it makes the desized fibrous material unsuitable for certain applications.

Recently a new technique of preventing the strength loss of thermally desized fibrous glass material has been developed. In this process the sized material treated with a salt comprising an alkali metal cation such as potassium, cesium or rubidium, preferably in the form of a thermally decomposable oxygen-containing anion, is desized by firing between about 600 F. to 1300 F. for a short period of time to heat clean the glass and give it optimum strength.

While the described process has been successful in most respects, for certain high temperature applications it has been less than satisfactory. For example, after heating at temperatures of 1000 F. and above, the tensile strength of the treated fibrous glass drops significantly over what is obtained at the less efficient lower process temperatures. Similarly, the heating times at the elevated temperature is critical to strength properties.

After considerable experimental work, it has been discovered that the above disadvantages and limitations can be obviated by a novel process described subsequently.

It is therefore an object of this invention, among many others, to thermally desize fibrous siliceous materials without substantially reducing the strength of the heat treated material.

It is an additional object of this invention to produce thermally desized fibrous materials by effecting thermally induced ion exchange of monovalent cations contained in the siliceous material with polyvalent cations.

Another object of this invention is the development of a process whereby a sized siliceous substrate containing monovalent cations is treated with a composition containing at least one polyvalent cation selected from Groups lI-A and Ill-B of the Periodic Table and possessing a larger atomic radius than sodium, is exposed to elevated temperatures until the sizing is removed and a substantial replacement of monovalent cations with the enu merated polyvalent cations takes place through thermally induced ion exchange.

A more particular object of this invention is the utilization of the above-described thermal desizing process wherein the treating composition includes an appropriate fluxing substance which reduces the melting point of the treating composition and permits its use at lower process temperatures.

An even more specific object of this invention described above is application of a treating composition comprising (a) at least one polyvalent cation selected as described above, combined with (b) at least one fluxing additive selected from the group consisting of sodium, potassium, rubidium and cesium.

An additional object of this invention is the development of a modified thermal ion exchange process wherein the strengthening process is conducted within or below the temperature range normally required for desizing so that reversible migration of the desired polyvalent cations does not take place and maximum strength is retained.

Further objects are the development of novel desizing processes, the preparation of heat cleaned white fibrous products possessing favorable physical properties for high temperature applications and the preparation of fibrous glass substrates impregnated with a mixture of polyvalent and monovalent cations which can be stored until needed, then thermally treated to produce desized siliceous products.

Additional objects will become apparent to the skilled reader after a perusal of this invention.

In practice, a fibrous siliceous substrate to be heat cleaned and containing replaceable monovalent cations, is contacted with a strengthening composition comprising at least one polyvalent cation, then heated to a temperature and for a time sufficient to substantially effect thermally induced ion exchange resulting in a heat cleaned substrate possessing high tensile strength. Following the high temperature firing step the fibrous substrate is usually washed with water to remove soluble salts which are present. However, for some purposes it may be desirable to incorporate an acid such as acetic acid into the wash and/or to heat the wash liquid up to boiling to effect more efficient washing. In addition, wetting agents may also be incorporated into the wash liquid to improve the effect of the Washing step. The fibrous material is then subjected to the usual finishing operations practiced in the art.

In the favored process, a glass fabric containing replaceable sodium cations and one or more thermally destructible contaminants such as sizing and lubricants, is contacted with a strengthening composition melting below about 1000 F., said strengthening composition comprising at least one polyvalent cation selected from Groups II-A and III-B of the Periodic Tables, said cation having a larger atomic radius than the sodium cation. The anionic portion of the polyvalent ion is preferably an oxygen-containing salt which produces oxygen upon heating at elevated temperatures. After drying, the glass fabric is heated from about 600 F. to about 1300 F., preferably from about 900 F. to about 1200 F., until a substantial portion of the monovalent ions in the fabric have been replaced with polyvalent cations.

The success of the inventive process is predicated upon the unexpected and substantial gain in physical properties obtained in the final product when the fibrous siliceous substrate impregnated with an excess of at least one polyvalent cation prior to firing, is heated at a temperature and time sufficient to displace smaller monovalent atoms such as hydrogen and sodium with larger sized polyvalent cations, and burn off the sizing. Therefore, no particular theory or mechanism is postulated. However, it may be constructive in the understanding of the instant invention to consider the fibrous substrate prior to firing as containing mobile, replaceable monovalent cations such as so dium and/or hydrogen interspersed in the network formers of the glass structure. During the heating of the substrate impregnated with less mobile polyvalent cations of larger diameter, the smaller monovalent cations are displaced by the larger, less mobile polyvalent cations through thermally induced ion exchange and a stronger article is produced.

A listing of Groups II-A and IIIB polyvalent cations, along with cations of group I-A are arranged below in the order of their atomic radii.

TABLE I.NON-POLAR COVALENT RADII OF THE ELEMENTS [From Chemical Periodicity, Sanderson, Library of Congress Catalog CardNo. (50-11081, page 26, FIGURES 24] The preferred polyvalent cations are calcium, barium, strontium, lanthanum and their mixtures.

Illustrative anions among many others are the nitrate, chlorate, iodate, bromate, perchlorate, persulfate, carbonate, phosphate, sulfate, acetate, formate and the like. For the most effective results the anionic portion of the polyvalent cation should be an oxygen-containing molety which can be thermally decomposed to release oxygen. These oxygen-releasing anions are preferred since they catalyze the removal of sizing and other components at firing temperatures lower than usually required. The anions can be in the form of simple salts, double salts, complex salts or mixtures of one or more salts, as long as they decompose at or below the firing temperature to produce oxygen.

As previously described in the favored process embodiment, good products are obtained wherein the firing of the substrate is conducted in the presence of at least one polyvalent cation of relatively low mobility; however, certain modifications can be employed which greatly enhance the physical properties of the fired fibrous substrate and for this reason are considered the preferred embodiment.

In the preferred embodiment a fibrous glass substrate to be heat cleaned is contacted with a strengthening composition melting below the upper temperature range used in the burning off process. In addition to the requisite polyvalent cation, the preferred compositions comprise one or more fiuxing substances which exert a eutectic effect upon the composition, particularly when the relatively high melting Group II-A oxygen-containing salts are employed. While these eutectic type additives can be selected from a variety of substances, particularly good results have been obtained when an oxygenated potassium salt is incorporated with the polyvalent cation into the strengthening composition.

The concentration of polyvalent cations used to treat the fibrous substrates in the favored and preferred. embodiments is not critical to the invention as long as sufficient cations are applied to assure the replacement of the monovalent cations such as sodium with the polyvalent cations. Ordinarily the substrate is treated with from about 0.5 to about 10% by weight, of treating salt in the form of an aqueous solution to obtain a pickup of about 0.l.53.0%, by weight, of cation. Since the cost of the polyvalent cations is low, a large excess of polyvalent cations, over the required quantities can be applied without deleterious efliect. The ratio of the eutectic additive to polyvalent cation is a variable depending upon several factors including the polyvalent cation, the additive employed and the temperature at which the treating process is conducted. For this reason no precise ratio of additive to polyvalent cation is suggested. However, when potassium nitrate is used as the additive the ratio of potassium to polyvalent cation ranges from about 0.5 part by weight to 2.0 parts by weight of potassium to each part by weight of polyvalent cation.

The strengthening compositions can be applied by a variety of techniques in a number of different forms. A convenient method is to apply the compositions in the form of their aqueous solutions. However, mixtures of acids and water, alcohol and water with or without acids or other solubilizing agents can be utilized. When the cations are applied in the form of their aqueous solutions any conventional application technique such as padding, dipping, spraying, coating, etc., can be used. Various adjuvants or additives such as softeners, surface active agents and the like, which will aid in the uniform application of the cations to the fibrous substrates can be incorporated into the application solution.

The salts can also be applied to the fibrous substrate in treatment 6, a 4% aqueous solution is used. In the first five treatments, a wet pickup, approximately resulted in a dry concentration of approximately 0.60%, by weight, of the salt while in the sixth treatment a dry concentration of 1.2% is obtained.

The dried fabric is heat cleaned at the temperatures set forth in Table II, and the thermally desized fabric washed with 3% acetic acid, rinsed with water and finished with an acrylic latex finish to protect the fibers against selfabrasion.

in the form of a fused melt or can be applied in granular form, then melted to impregnate the yarns. Alternatively, the salts can be added to the starch-oil size which is commonly applied to fiber glass yarns in the first step of their manufacture. This is useful since the salts are present on both warp and fill yarns and obviates an additional application step.

The salts can also be applied to the warp yarns only during the conventional warp sizing step. For treatment in this manner, the salts are added as a component to warp sizing and the yarns treated in the usual manner. When applied in this manner, the salts are present on the warp yarns with the sizing materials. The fabric is then woven and fired to produce the improved, heat cleaned substrate. In some instances, depending upon the substrate, the presence of the polyvalent salts can also exert a favorable effect on the untreated fill yarns.

While it is convenient to apply the strengthening composition at the stages described above, the cations can be applied at any stage of fabric manufacture prior to heat cleaning. These include fibers, yarns, rovings, etc. As indicated earlier the inventive process is applicable to fibrous and siliceous materials, including all types of fiber glass which in contrast to massive or cast glass can be made into fabrics.

The temperature of the heat cleaning, desizing or firing step can vary widely according to the particular siliceous substrate employed, the sizing or other additives present, the cations applied during treatment, the length of heating and the effect sought. Ordinarily the temperature will vary between about 600 F. to about 1300 F. with the greatest benefits under the present invention being obtained at temperatures ranging between about 900 F. and 1200 F.

The firing time is not critical and as previously stated is dependent upon the firing temperature and the end use to which the product is to be put. The broad range of exposure time can range from fractions of a second to about 24 hours or even more. More conventionally the heat treatment will vary between about a second and several hours.

The mode of heating is not important; any suitable heat treating device such as ovens and/or furnaces can be effectively used. These include forced air ovens and mufile furnaces and the like.

To illustrate this invention in the greatest possible detail the following examples are submitted:

EXAMPLE I In this example, a casement style E glass fabric of Style S/473 (4.4 oz. per sq. yd., 150 1/0) containing sizing is treated in a textile padder with aqueous solutions of the nitrate salts shown in the table below. In the first five treatments, 2% aqueous solutions are employed, while From the results shown above, it can be seen that Samples 3-6, each treated with the salt solutions of this invention, exhibit improved tensile strength properties compared to the control. Sample 2, had poor strength characteristics compared to the control-this is attributed to the fact that the sodium cation is replaced with a magnesium cation of smaller atomic radius, presumably resulting in the production of an inferior and weakened fabric. All products exhibited excellent whiteness.

In a related experiment, the casement style glass fabric of Style 5/473 is treated with a solution comprising 1% NaNO 1% KNO 1.6% Ca(NO -4H O and 0.4% Ba(NO Good tensile strength retention is obtained after heat cleaning for 4 seconds at 1060 F.

EXAMPLE II Average Tensile Strength, lbs. linclt width Warp Direction Fill Direction Temperature:

1,020 F 204 162 194 160 194 IFS 192 174 206 161 EXAMPLE III Style 8/604 (a 12 oz./sq. yd. E glass air filtration fabric 42 x 30 warp 1502/2 filling l/4, 9% bulked yarn) is treated with an aqueous solution containing 2% KNO3, and BPI(NO3)2.

The fabric is dried and then heat cleaned for 15 seconds at 1080 F. The fabric is washed with 3% acetic acid, rinsed with water and redried. After finishing with a phenyl methyl silicone emulsion the fabric was tested for tensile strength with the following results:

S 604 Tensile Strength, lbs/inch width Warp Direction Fill Direction As per Example III .2 487 156 Greige Fabric, Untreated. 460 158 In Example II the fabric treated at 1080 F. has a warp tensile strength of 192 as compared to 206 for the greige. In Example III the 1080 F. fabric had a warp tensile strength of 487 as compared to 466 for the greige.

In an experiment comparable to Example III, a woven quartz fabric containing sizing treated with 2% aqueous solutions of barium, calcium and potassium nitrate is dried, heat cleaned at 1080 F., washed with 3% acetic acid and finished as described. Comparable retention of tensile strength is obtained.

As the previous discussion and enumerated examples indicate, numerous advantages are derived from the practice of this invention, both in its product and process aspect. For example, the fired fibrous siliceous product is a white material, free from sizing and other degradable products which retains a substantial portion of the original greige strength upon finishing. By substantial portion of greige strength is meant at least 80% of the original greige fabric strength when finished. In addition, the products of this invention lend themselves for applications as laminating substrates. Further, the substrates impregnated with polyvalent cations, but unfired, can be stored for long periods of time until required.

In its process aspects, the invention is advantageous in several respects. These include economy and simplicity of operation, relatively mild process conditions and short process cycles. In addition, the process yields reproducible and reliable products employing readily available starting materials and process equipment.

Additional advantages will be gleaned after a perusal of this invention.

As the specification and above discussion indicates, various modifications and changes can be made in this invention without departing from the inventive concept. The metes and bounds of the invention are illustrated by the claims which follow.

What is claimed is:

1. A process for heat treating sized fibrous siliceous substrates containing monovalent cations without causing substantial degradation of the tensile strength, comprising the steps of:

(a) treating the fibrous siliceous substrates with a mixture of cations having an atomic radius at least as large as sodium, said mixture comprising at least one polyvalent cation, and at least one monovalent cation selected from the group consisting of sodium, potassium, rubidium, cesium and mixtures of these cations, and

(b) heating the treated fibrous siliceous substrates while dry until substantially all of the sizing is removed.

2. A desized fibrous siliceous substrate produced by the process of claim 1.

3. A process for heat treating sized fibrous siliceous substrates containing sodium cations between about 600 F. to 1300 F. without causing substantial degradation of tensile strength, comprising the steps of:

(a) treating the fibrous siliceous substrates with a composition containing at least one polyvalent cation having an atomic radius larger than sodium, said polyvalent cation being selected from Groups II-A 8 and III-B of the Periodic Table, and at least one monovalent cation selected from the group consisting of sodium, potassium, rubidium, cesium and mixtures of these cations, and

(b) heating the treated fibrous substrate while dry between about 600 F. to about 1300 F. until substantially all of the sizing is removed.

4. The process of claim 3 wherein the Group II-A and III-B polyvalent cations are selected from the group consisting of calcium, strontium, barium, lanthanum and mixtures of these polyvalent cations.

5. A process for thermally desizing a fibrous glass substrate containing sodium cations between about 900 F. and 1200 F. without causing substantial degradation ot tensile strength, comprising the steps of:

(a) treating a fibrous glass substrate with a composition comprising at least two polyvalent cations having an atomic radius larger than sodium, said polyvalent cation being selected from Groups II-A and IIIB of the Periodic Table, at least one monovalent cation selected from the group consisting of sodium, potassium, rubidium, cesium and mixtures of these cations, and at least one oxygen containing anion, said composition melting between about 900 F. to 1200 F., and

(b) heating the treated fibrous glass substrate while dry between about 900 F. and l200 F. until the substrate is desized and retains a substantial portion of the original greige strength when. finished.

6. The process of claim 5 wherein the treating composition includes at least one monovalent cation selected from the group consisting of sodium, potassium, rubidium, cesium, and mixtures of these cations and at least two polyvalent cations having an atomic radius larger than sodium, said polyvalent cations being selected from Group IIA of the Periodic Table.

7. The process of claim 6 wherein the treating composition contains barium nitrate, calcium nitrate and potas sium nitrate.

8. The process of claim 6 wherein the ratio of monovalent cation to polyvalent cations ranges from about 0.5 to about 2 parts, by weight, of monovalent cation to each part, by weight, of polyvalent cation.

References Cited UNITED STATES PATENTS 2,674,549 4/1954 Balz 134-2 2,779,136 l/l957 Hood et al. 3,232,788 2/1966 Marzocchi et al.

OTHER REFERENCES Stresses in Glass Produced by Nonunitorm Exchange of Monovalent Ions, pages 59-63, vol. 45, No. 2, of the Journal of Pm. Ceramic Society by S. S. Kistler.

Measurement of the Mechanical Strength of Glass After Reinforcement; U.S.C.V. Symposium sur la Resistance by P. Aclogue and J. Tochon.

DONALL H. SYLVESTER, Primary Examiner.

R. L. LINDSAY, Assistant Examiner. 

